1. Field of the Invention
The present invention relates generally to the field of location (or position) determination, and more particularly to portable User Equipment (UE) adapted to provide a user with an indication of current location.
2. Description of the Related Art
Global Navigation Satellite Systems (GNSS) are well known, as is a portable or mobile UE for use with such systems. These GNSS systems include Global Positioning System (GPS), GLObal NAvigation Satellite System (GLONASS), Galileo, and a compass system (also known as Beidou-2, BD2). Typically, an array (or constellation) of satellites, which are commonly referred to as Space Vehicles (SVs), is arranged to transmit navigation signals for reception by the UE, and from the received navigation signals the UE will calculate its current position. In other words, the UE processes the received signals and makes a location determination yielding an indication of current location.
A plurality of such navigation signals must be received for the UE to be able to calculate its location from just those signals. For example, when using the GPS system, the minimum number of signals required, at least from start-up (or during any other acquisition phase), is four. That is, the UE needs to receive signals from four separate SVs at a particular location in order to make an accurate position determination.
If fewer than the minimum number of signals are received at a particular location, the UE cannot make a position determination. When this occurs, the UE may simply continue to present the user with an indication of the last known position, but this of course has disadvantages. Alternatively, the UE may present a user with a “position unknown” message, but this is also undesirable.
UEs that operate with both GNSS and cellular communications systems (including networks) are also known. Such a UE can take the form of a GPS capable device, which also functions as a mobile phone. It is known for such a UE to be able to determine an identity of a cell of the communication system in which the UE is currently located from a signal or signals received from the system. That is, cellular systems, such as terrestrial communication systems, commonly transmit signals including information indicative of the cell in which they are being transmitted.
With these dual-system devices, it is known for the UE, when at a location in which it is unable to determine a location from received navigation signals (for example, because too few are currently being received), to provide the user with an indication of the cell in which the UE is currently located. Although offering some improvement over a simple “position unknown” signal, this technique still has disadvantages; for example, the user is not provided with an accurate enough indication of position, as the cell covers a wide area.